H. Wagner: Structure and Healing of Bone as a Response to Strain and Stress 93 



mycin administration, is three to five times greater at the metaphysis than at the dia- 

 physeal level in both the inert and the loaded bones. 



As previously observed by Vigliani (1955 a, b) in the dog, and in the rat by 

 Landry and Fleisch (1962, 1964), three successive stages can be distinguished in the 

 response of shaft bones to unloading and/or denervation. We observed an initial 

 stage, characterised by increased resorption and temporary decrease of bone tissue 

 deposition; a second stage, in which both resorption and apposition of new bone are 

 increased. During this period, the difference in the relative amount of new formed 

 bone in the homotypic bones of the inert and mobile limb are greatest; a third stage, 

 in which both bone resorption and deposition are greater in the inert than in the 

 mobile bones, but a decrease of bone turnover occurs in comparison to the second 

 stage. 



These quantitative changes in bone apposition and bone turnover due to un- 

 loading and denervation are not paralleled by qualitative changes in structures of the 

 2nd and 3rd order. Amprino (1938) has shown in man and Vigliani (1955 b) in the 

 dog that normally structured osteones are formed and renewed in the cortex of bones 

 rendered mechanically inert for long periods of time. Hence, the stresses normally 

 undergone by skeletal components at rest and in motion do not appear to be strictly 

 necessary for the formation of normally structured and normally arranged bone 

 tissue, once the general pattern of bone architecture has been laid down. 



It may, therefore, be claimed that bones, which no longer serve their normal 

 mechanical function, can participate to a greater extent than normally loaded and 

 innervated bones in the mineral metabolism of the organism, acting as stores of in- 

 organic and organic materials and undergomg contmuous turnover. 



References 



Amprino, R.: La struttura delle ossa deiruomo sottratte alle sollecitazioni nieccaniche. Arch. 



Entwickl.-Mech. Org. 138, 305 (1938). 

 Landry M., and H. Fleisch: Influence de rimmobilisation sur la formation et la destruction 



osseuse evaluees par I'incorporation des tetracyclines dans I'os. Helv. physiol. pharmacol. 



Acta 20, C 69 (1962). 



— — The influence of immobilisation on bone formation as evaluated by osseous incorpo- 

 ration of tetracyclines. J. Bone Jt Surg. 46 B, 764 (1964). 



Vigliani, F.: Accrescimento e rinnovamento strutturale della compatta in ossa sottratte alle 

 sollecitazioni meccaniche. Nota I. Z. Zellforsch. 42, 59 (1955 a). 



— Accrescimento e rinnovamento strutturale della compatta in ossa sottratte alle sollecita- 

 zioni meccaniche. Nota II. Z. Zellforsch. 43, 17 (1955 b). 



Structure and Healing of Bone as a Response to Continuous 

 and Discontinuous Strain and Stress 



H. Wagner 



Orthoplidische Universitatsklinik Miinster, Deutschland 



The structure of bone tissue is a response to the forces of stress and strain, these 

 control the disposition of the trabeculae in cancellous bone as well as the orientation 

 of the Haversian systems in compact bone. A change of the direction of force causes 

 an alteration of the bone structure. 



